The long-term objective of this research is a detailed understanding of herpes virus DNA polymerases and drugs that target them. These enzymes, which include a catalytic subunit (Pol) and an accessory subunit that stimulates long-chain DNA synthesis, are both prototype [unreadable].-like DNA polymerases and excellent targets for antiviral drugs. This latter property is especially health-related, as new drugs are needed for treatment of herpes virus infections. In this application, unanswered questions regarding accessory subunits, catalytic subunits, and drugs that target these proteins and their interaction are addressed. Specific aim 1 is to investigate the unusual and different manners by which the accessory subunits, herpes simplex virus (HSV) UL42 and human cytomegalovirus (HCMV) UL44, interact with DNA so that they bind tightly, yet diffuse linearly along the DNA to permit possessive DNA synthesis. Single-molecule approaches will be used to analyze how these proteins move on DNA, particularly whether UL44 "slides" or whether it "hops" like UL42, and whether these proteins necessarily move helically or can, for example, move along one side of the helix. The force required to move these subunits will be assessed. Studies will be initiated to measure the force required to stop or slow the catalytic subunits, and to optimize crystallization conditions of protein-DNA complexes in preparation for structure determination. Specific aim 2 is to investigate the roles of structural domains of the catalytic subunits that are N-terminal to the thumb, palm, and fingers domains in terms of enzymatic functions, viral replication, and mechanisms of antiviral drug resistance. Two structural domains, pre-NH2 and NH2, have been observed in the crystal structure of HSV Pol, but their roles in enzyme function and viral replication are unknown. Additionally, the mechanisms by which mutant HCMV Pols with substitutions in their 3'-5'exonuclease domain resist ganciclovir (GCV) action are not understood. To address these questions, mutant enzymes will be engineered and assayed for relevant enzyme activities. Interesting HSV pol mutations will be engineered into mutant viruses in preparation for assays of their effects on viral replication. Specific aim 3 is to study the mechanisms of promising new compounds that inhibit the interaction of HCMV Pol and UL44 and HCMV replication. A combination of genetic, virological, biochemical, and crystallographic approaches will be initiated. Efforts to discover new agents that exploit this interaction (and to understand their mechanisms) will also begin.